Experiments were conducted in a rotating two-pass cooling channel with an aspect ratio of 2:1 (Dh = 16.9 mm). Results for two surface conditions are presented: smooth and one ribbed configuration. For the ribbed channel, the leading and trailing walls are roughened with ribs (P/e = 10, e/Dh = 0.094) and are placed at an angle (α = 45°) to the mainstream flow. For each surface condition, two angles of rotation (β = 90°, 135°) were studied. For each angle of rotation, five Reynolds numbers (Re = 10K–40K) were considered. At each Reynolds number, five rotational speeds (Ω = 0–400 rpm) were considered. The maximum rotation number and buoyancy parameter reached were 0.45 and 0.85, respectively. Results showed that rotation effects are minimal in ribbed channels, at both angles of rotation, due to the strong interaction of rib and Coriolis induced vortices. In the smooth case, the channel orientation proved to be important and a beneficial heat transfer increase on the leading surface in the first pass (radially outward flow) was observed at high rotation numbers. The correlations developed in this study for predicting heat transfer enhancement due to rotation using the buoyancy parameter showed markedly good agreement with experimental data (+/-10%). Finally, heat transfer under rotating conditions on the tip cap showed to be quite dependent on channel orientation. The maximum tip cap Nu/Nus ratio observed was 2.8.
Flow in the internal three-pass serpentine rib turbulated passages of an advanced high pressure rotor blade is simulated on a 1:1 scale in the laboratory. Tests to measure the effect of rotation on the Nusselt number are conducted at rotation numbers up to 0.4 and Reynolds numbers from 75,000 to 165,000. To achieve this similitude, pressurized Freon R134a vapor is utilized as the working fluid. Experimental heat transfer coefficient measurements are made using the copperplate regional average method. Regional heat transfer coefficients are correlated with rotation numbers. An increase in heat transfer rates due to rotation is observed in radially outward passes; a reduction in heat transfer rate is observed in the radially inward pass. Strikingly, a significant deterioration in heat transfer is noticed in the “hub” region — between the radially inward second pass and the radially outward third pass. This heat transfer reduction is critical for turbine cooling designs.
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